Average Weather in Chicago Illinois, United States

In Chicago, the summers are warm, humid, and wet; the winters are freezing and windy; and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 22°F to 83°F and is rarely below 5°F or above 91°F.

Based on the tourism score, the best time of year to visit Chicago for warm-weather activities is from mid June to mid September.

Temperature

The warm season lasts for 3.6 months, from June 3 to September 20, with an average daily high temperature above 73°F. The hottest day of the year is July 19, with an average high of 83°F and low of 71°F.

The cold season lasts for 3.2 months, from December 2 to March 9, with an average daily high temperature below 43°F. The coldest day of the year is January 29, with an average low of 22°F and high of 33°F.

The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Clouds

In Chicago, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.

The clearer part of the year in Chicago begins around June 11 and lasts for 4.5 months, ending around October 29. On August 27, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy68% of the time, and overcast or mostly cloudy32% of the time.

The cloudier part of the year begins around October 29 and lasts for 7.4 months, ending around June 11. On December 29, the cloudiest day of the year, the sky is overcast or mostly cloudy59% of the time, and clear, mostly clear, or partly cloudy41% of the time.

The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Chicago varies throughout the year.

The wetter season lasts 7.0 months, from March 29 to October 31, with a greater than 26% chance of a given day being a wet day. The chance of a wet day peaks at 37% on May 27.

The drier season lasts 5.0 months, from October 31 to March 29. The smallest chance of a wet day is 15% on January 30.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 37% on May 27.

The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Chicago experiences significant seasonal variation in monthly rainfall.

Rain falls throughout the year in Chicago. The most rain falls during the 31 days centered around June 1, with an average total accumulation of 3.7 inches.

The least rain falls around January 27, with an average total accumulation of 0.9 inches.

Average Monthly Rainfall

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Snowfall

We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.

As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Chicago experiences some seasonal variation in monthly liquid-equivalent snowfall.

The snowy period of the year lasts for 3.5 months, from December 2 to March 19, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around February 1, with an average total liquid-equivalent accumulation of 0.3 inches.

The snowless period of the year lasts for 8.5 months, from March 19 to December 2. The least snow falls around July 24, with an average total liquid-equivalent accumulation of 0.0 inches.

The average liquid-equivalent snowfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average rainfall.

Sun

The length of the day in Chicago varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 8 minutes of daylight; the longest day is June 21, with 15 hours, 14 minutes of daylight.

The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise is at 5:14 AM on June 14, and the latest sunrise is 2 hours, 11 minutes later at 7:25 AM on November 3. The earliest sunset is at 4:19 PM on December 8, and the latest sunset is 4 hours, 10 minutes later at 8:29 PM on June 27.

Daylight saving time (DST) is observed in Chicago during 2018, starting in the spring on March 11, lasting 7.8 months, and ending in the fall on November 4.

The solar day over the course of the year 2018. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight saving time are indicated by the 'DST' labels.

Humidity

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The muggier period of the year lasts for 3.6 months, from June 4 to September 22, during which time the comfort level is muggy, oppressive, or miserable at least 12% of the time. The muggiest day of the year is July 27, with muggy conditions 50% of the time.

The least muggy day of the year is February 10, when muggy conditions are essentially unheard of.

The percentage of time spent at various humidity comfort levels, categorized by dew point.

Wind

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Chicago experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 7.1 months, from October 1 to May 6, with average wind speeds of more than 11.4 miles per hour. The windiest day of the year is January 4, with an average hourly wind speed of 14.4 miles per hour.

The calmer time of year lasts for 4.9 months, from May 6 to October 1. The calmest day of the year is August 3, with an average hourly wind speed of 8.5 miles per hour.

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The predominant average hourly wind direction in Chicago varies throughout the year.

The wind is most often from the north for 1.7 months, from March 6 to April 27, with a peak percentage of 29% on March 10. The wind is most often from the south for 6.7 months, from April 27 to November 19, with a peak percentage of 36% on September 7. The wind is most often from the west for 3.6 months, from November 19 to March 6, with a peak percentage of 41% on January 1.

Wind Direction

The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions, excluding hours in which the mean wind speed is less than 1.0 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Water Temperature

Chicago is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average water temperature experiences significant seasonal variation over the course of the year.

The time of year with warmer water lasts for 2.7 months, from July 4 to September 25, with an average temperature above 65°F. The day of the year with the warmest water is August 12, with an average temperature of 72°F.

The time of year with cooler water lasts for 4.9 months, from December 12 to May 10, with an average temperature below 43°F. The day of the year with the coolest water is March 1, with an average temperature of 35°F.

The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.

Best Time of Year to Visit

To characterize how pleasant the weather is in Chicago throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Chicago for general outdoor tourist activities is from mid June to mid September, with a peak score in the last week of August.

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Chicago for hot-weather activities is from early July to late August, with a peak score in the last week of July.

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Growing Season

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in Chicago typically lasts for 7.2 months (222 days), from around April 2 to around November 10, rarely starting before March 15 or after April 19, and rarely ending before October 23 or after November 30.

The percentage of time spent in various temperature bands. The black line is the percentage chance that a given day is within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

Based on growing degree days alone, the first spring blooms in Chicago should appear around April 19, only rarely appearing before April 4 or after May 4.

The average growing degree days accumulated over the course of the year, with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.

The brighter period of the year lasts for 3.5 months, from May 6 to August 21, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest day of the year is July 1, with an average of 7.0 kWh.

The darker period of the year lasts for 3.3 months, from November 2 to February 12, with an average daily incident shortwave energy per square meter below 2.7 kWh. The darkest day of the year is December 22, with an average of 1.6 kWh.

The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

For the purposes of this report, the geographical coordinates of Chicago are 41.850 deg latitude, -87.650 deg longitude, and 594 ft elevation.

The topography within 2 miles of Chicago is essentially flat, with a maximum elevation change of 69 feet and an average elevation above sea level of 591 feet. Within 10 miles is essentially flat (253 feet). Within 50 miles contains only modest variations in elevation (653 feet).

The area within 2 miles of Chicago is covered by artificial surfaces (100%), within 10 miles by artificial surfaces (66%) and water (34%), and within 50 miles by water (36%) and artificial surfaces (29%).

Data Sources

This report illustrates the typical weather in Chicago, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.

Temperature and Dew Point

There are 4 weather stations near enough to contribute to our estimation of the temperature and dew point in Chicago.

The estimated value at Chicago is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Chicago and a given station.

Other Data

All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.

Disclaimer

The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.

We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.

We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.